If the SDK can’t find any available tracker, the operation “FindAllEyeTrackers” will return an empty list. Here is a little larger example that handles this problem a little more gracefully. I just tested it with a Tobii X120 connected directly to a USB/Ethernet adapter in my laptop:
https://gist.github.com/jonashogstrom/baed7fbc9cab4f2464773234748bd34f